1. Field of the Invention
The present invention relates to the field of semiconductor substrate processing equipment. More particularly, the present invention relates to an apparatus and method for aligning a substrate and a shield member on a support member.
2. Background of the Related Art
In the fabrication of integrated circuits, equipment has been developed to automate substrate processing by performing several sequences of processing steps without removing the substrate from a vacuum environment, thereby reducing transfer times and contamination of substrates. Such a system has been disclosed for example by Maydan et al., U.S. Pat. No. 4,951,601, in which a plurality of processing chambers are connected to a transfer chamber. A robot in a central transfer chamber passes substrates through slit valves in the various connected processing chambers and retrieves them after processing in the chambers is complete.
The processing steps carried out in the vacuum chambers typically require the deposition or etching of multiple metal, dielectric and semiconductor film layers on the surface of a substrate. Examples of such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), and etching processes. Although the present invention pertains primarily to CVD processes, it may have application to other processes as well.
CVD vacuum chambers are employed to deposit thin films on semiconductor substrates. Typically, a precursor gas is charged to a vacuum chamber through a gas manifold plate situated above a substrate. The substrate is heated to process temperatures. The precursor gas reacts. on the heated substrate surface to deposit a thin layer of material thereon. In a typical process chamber, a support member on which a substrate is mounted during processing is movable vertically in the chamber by means of a vertically movable support member. A plurality of support fingers are also vertically movable by an elevator and extend through the support member to facilitate transfer of the substrate from a robot blade onto the support member.
A number of problems associated with the deposition of the film of material on the substrate are at least partially attributable to improper alignment and shielding of the substrate. One such related problem occurs when the material deposits on the edge and back side surfaces of the substrate. Typically, these edge and back side surfaces are rougher than the highly polished top surface and are not coated with the adhesive layer covering the top surface. Therefore, material deposited on these surfaces tends to flake off the substrate and create particles. Generation of particles within the chamber is to be avoided as the particles may contaminate the substrates being processed and, thereby reduce the yield of good devices, and may damage the chamber components. Another problem occurs when the material deposits on the back side of the substrate causing the substrate to stick to the support member. Sticking may lead to particle generation when the deposited material adhering the substrate to the support member is broken away during removal of the substrate from the chamber
An additional concern relating to alignment and shielding pertains to the industry demands for film uniformity and edge exclusion. As the desire for greater throughput and efficiency has increased, the standards governing the placement and thickness of the deposited film at the substrate edge have continually become more stringent. Ideally, the deposited film has a uniform thickness across the entire area of the substrate with the edges of the film dropping off rapidly so that the zone of exclusion has little or no deposition thereon. Further, there is ideally no deposition on the beveled edges of the substrate. Industry practice has moved toward this ideal goal so that the current industry standards demand no film deposition on the beveled edge of the substrate and a film thickness at a point 3 mm from the edge of the substrate that is 90 percent or more of the film thickness at the center of the substrate with a thickness uniformity of .+-.5 percent, excluding the area within 5 mm from the substrate edge. To achieve these requirements, the substrate must be properly aligned on the support member with the edges properly shielded.
In an effort to overcome the above mentioned problems, various devices and methods have been developed to shield the edge and back side surfaces of the substrate and to provide proper alignment of the substrate relative to the support member and other chamber components. Included among these devices are shadow rings, shielding purge gases and their delivery systems, and alignment mechanisms, such as guide pins. Shadow rings and purge gases are used to prevent deposition of the material on the edge and back side surfaces of the substrate; whereas, guide pins are used to align the substrate on the support member.
Shadow rings cover the periphery of the substrate during deposition to mask the edge of the substrate, thereby preventing the deposition gases from reaching the edge and back side surfaces of the substrate. To obtain the required edge exclusion, the substrate and the shadow ring must be properly aligned relative to one another and relative to the support member. Typically, the shadow ring is supported in the chamber by an outer support ring above the support member during substrate transfer and is lifted by the support member when the support member lifts the substrate into the upper portion of the chamber where the deposition of the film occurs. Therefore, because the shadow ring is removed from the support member during each process cycle, the shadow ring may become misaligned relative to the support member and a properly aligned substrate on the support member. Accordingly, an alignment mechanism for ensuring alignment of the shadow ring to the support member and the substrate is needed.
The shielding purge gas is directed about the periphery of the substrate and exerts a positive pressure that reduces the chance that processing gas will reach the edge and back side surfaces of the substrate. To provide the purge gas to the full periphery of the substrate, the support member typically includes an annular gas groove that has an inner diameter that is less than the outer diameter of the substrate and an outer diameter that is greater than the outer diameter of the substrate so that a properly aligned substrate resting on the upper surface of the substrate overhangs the gas groove about the full periphery of the substrate. It has been found that the combination of a shadow ring and a purge gas further enhance edge performance.
Although a number of alignment mechanisms are presently in use and many of the prior alignment mechanisms are useful in connection with the present invention, the following description focuses primarily on an alignment mechanism using guide pins. An alignment mechanism using guide pins employs a plurality of guide pins extending upwardly from the upper surface of the support member. The guide pins are equally spaced about the periphery of the support member and have an inner angled surface that flares outwardly toward their upper ends. The guide pins are sufficiently spaced so that they can receive a substrate therebetween. The guide pins act as a funnel that centers the substrate on the support member as the support member moves to receive the substrate thereon. So that the substrate is properly positioned with its full peripheral edge overhanging the gas groove, the guide pins extend from the outer periphery of the gas groove and partially overhang the gas groove. In this way, the lower end of the funnel defined by the plurality of guide pins has a diameter that is intermediate the inner and outer diameters of the gas groove and that is larger than the outer diameter of the substrate. Accordingly, as the support member moves upwardly to receive the substrate thereon, the angled walls of the guide pins force the substrate laterally into alignment and so that it overhangs the gas groove about the full periphery of the substrate.
However, the guide pins used to force the substrate laterally into alignment necessarily abut the edge of the substrate to obtain this alignment and remain in abutment therewith when the substrate rests upon the upper surface of the support member. The purge gas flowing from the gas groove cannot flow between the guide pins, which are attached to the upper surface of the support member, when the substrate and guide pins are in abutment with one another. Therefore, the contact between the guide pins and the substrate prevents the purge gas from shielding the edge of the substrate proximal the guide pins in abutment with the substrate and permits deposition of the film in the vicinity of the abutting guide pins. Thus, the blockage caused by contact between the guide pins and the substrate edge allows the film to deposit in the exclusionary zone and on the beveled edge near the guide pins creating a danger of flaking and particle generation and preventing compliance with the industry requirements for edge exclusion.
Thus, despite the use of all of the prior art features, there remains a need for increasing proper alignment between a substrate, a support member, and a shadow ring. Additionally, there is a need for an alignment mechanism that does not adversely affect the flow of purge gas at the substrate edge.